Uranium Enrichment: How the Process Turns Natural Uranium Into Nuclear Fuel

Published: July 2026

Uranium enrichment is a key step in the front end of the nuclear fuel cycle. It increases the concentration of uranium-235, the isotope that most readily sustains the fission chain reaction used to generate heat in a nuclear reactor. Natural uranium contains about 0.7% uranium-235, with most of the rest made up of uranium-238.

Most commercial nuclear power plants cannot efficiently use natural uranium as fuel. Before it can be fabricated into reactor fuel, uranium is typically mined, milled into uranium concentrate, converted into uranium hexafluoride gas and then enriched to raise the share of uranium-235. For today’s light-water reactors, uranium is commonly enriched to about 3% to 5% uranium-235 before it is converted into uranium dioxide powder, pressed into ceramic pellets and loaded into fuel rods, according to the NRC and DOE.

The enrichment process does not create new uranium. Instead, it separates uranium isotopes based on small differences in atomic mass. In modern commercial enrichment, uranium hexafluoride gas is introduced into centrifuges that spin at high speed. The slightly heavier uranium-238 molecules move more toward the outer edge of the centrifuge, while gas containing more uranium-235 is drawn off as an enriched stream. The remaining material, with less uranium-235, is known as depleted uranium. DOE describes gas centrifuge enrichment as the process commercially used in the United States today. 

Enrichment is measured by the percentage of uranium-235 in the final uranium product. Low-enriched uranium, or LEU, is generally defined as uranium enriched to less than 20% uranium-235. Conventional reactor fuel is usually at the lower end of that range, around 3% to 5%. High-assay low-enriched uranium, or HALEU, is a subset of LEU enriched above 5% and below 20% uranium-235, according to the Department of Energy, the NRC and the World Nuclear Association.

The difference between standard LEU and HALEU matters because enrichment level affects fuel performance. A higher concentration of uranium-235 allows reactor designers to get more energy from a smaller amount of fuel. For many advanced reactor designs, HALEU can support smaller reactor cores, longer operating cycles, improved fuel utilization and higher power density, according to DOE and NRC.

HALEU is especially important for advanced reactors, including many small modular reactors, microreactors and non-light-water reactor concepts. Some designs use HALEU in ceramic-coated TRISO fuel particles, metallic fuel, molten salt fuel or other advanced fuel forms. The NRC notes that HALEU between 5% and 20% uranium-235 is proposed for many advanced non-light-water reactor designs, while DOE says most U.S. advanced reactors under development require HALEU to achieve smaller designs, longer cycles and greater efficiency. 

The supply chain for HALEU is more complex than simply enriching uranium to a higher level. It requires licensed enrichment capacity, conversion and deconversion capabilities, transportation packages approved for higher-assay material, fuel fabrication infrastructure and regulatory frameworks suited to new fuel forms. The World Nuclear Association notes that HALEU can be produced with existing centrifuge technology but requires specific fuel cycle infrastructure, licensing regimes and transport containers.

In the United States, HALEU availability remains a strategic constraint for advanced reactor deployment. DOE says HALEU is not currently available from domestic suppliers at commercial scale and has estimated domestic demand could reach 50 metric tons per year by 2035, with additional amounts needed thereafter. The agency is pursuing multiple supply pathways, including limited down-blending of existing government-owned material and enrichment demonstrations.

Read more:

• Energy.gov: HALEU Frequently Asked Questions
• Energy.gov: What is High-Assay Low-Enriched Uranium (HALEU)?

In simple terms, enrichment determines whether uranium can serve as fuel for a given reactor design. Standard enrichment supports today’s commercial nuclear fleet. HALEU extends that role to many next-generation reactors that need fuel capable of delivering more energy in smaller, more efficient systems. As advanced nuclear developers move from design to demonstration and deployment, enrichment capacity, especially HALEU enrichment, will be one of the most important links in the nuclear fuel supply chain.